The high combustion temperature of an internal combustion engine requires the heat to be removed to prevent damage to the pistons and cylinders. Indeed, with lighter weight aluminum heads (as opposed to heavier cast iron), the head material could melt without adequate cooling. In addition, excessive temperatures can break down oil, so that it does not perform its lubricating function. It is thus imperative to reject heat from an internal combustion engine, either through air cooling or fluid cooling (typically water combined with a chemical coolant additive).
Aircraft engines typically employ air cooling rather than water cooling due to the abundance of ram air and the extra weight occasioned by the radiator, water pump, coolant, reservoir, and other fluid cooling system hardware. For these reasons, radial engines were developed in order to leverage the available ram air.
In limited applications, such as the P-51 Mustang by Allison-Packard and certain Rolls Royce V-12 aircraft engines, water cooling was employed where a radial configuration was deemed to compromise aerodynamics. But those engines were configured as in-line blocks, which are not suitable for air cooling in the way radial engines are. For example, in a radial engine each cylinder is directly exposed to cooling air flow, whereas in an in-line engine (V-8, V-12) only the most forward facing cylinder is directly exposed to the ram air flow. For this reason, radial engine configurations have been used in aircraft.
There have also been a limited number of liquid cooled radial engines proposed for flight environments, such as the Wright Tornado R-2160 42 cylinder radial engine and the BMW 803 28 cylinder four row radial engine. However, all presently known known water cooled radial engines have been limited to aircraft (non-ground based) flight applications.
Kealy et al. U.S. Pat. No. 8,567,354, the entire disclosure of which is hereby incorporated herein, proposes an air cooled radial engine for use in a ground-based, portable energy generation system. The Kealy radial engine configuration employs air cooling, but is limited in its ability to reject heat in a ground based system at high ambient temperatures, especially at the exhaust valve ports. In addition, the large fan (e.g., 60 inches in diameter) required to move the cooling air (e.g., 22,000 cubic feet per minute (CFM)) created high ambient noise, which can be problematic in urban areas which may impose noise restrictions.
Systems and methods are thus needed which provide the horsepower-to-weight ratio available from a radial engine in a ground-based power generation system, but which avoid the limitations of air cooled systems.
Various features and characteristics will also become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background section.